Swivel joint for arms for electric lights



June 27, 1950 s. T. CEDERBORG 2513,1144

SWIVEL JOINT FOR ARMS FOR ELECTRIC LIGHTS Filed Feb. 16. 1945 E E5 E5 Attorney Patented June 27, 1950 SWIVEL JOINT FOR ARMS FOR ELECTRIC LIGHTS Stig Thorsten Cederborg, Stockholm, Sweden Application February 16, 1945, Serial No. 578,204 In Sweden January 4, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires January 4, 1964 6 Claims. 1

My invention relates to swivel joints for arms for electrical fixtures, particularly for electric lights.

Swivel joints in arms for electric lights have previously sometimes been made without any regard for the fact that the electrical conduit had to be carried through the arm and the swivel joint. In such cases the electrical conductors were passed out through an opening in the arm below the swivel joint and extended freely past the joint and into a second opening in the arm above the joint. This arrangement, however, from the point of security was very unsatisfactory, as the conductors, which usually were provided with relatively weak insulation when intended to be enclosed with pipes, were easily damaged .at their exposed parts around the joint. To a great extent this was particularly the case due to the reason that the joint could in certain positions he placed in such relation to the conduit that the'electrical conductors were placed outwardly of the convex part of the joint, said conductors thereby being placed on that side of the arm, which was subject to the greatest risk of blows and other mechanical effects.

It was hence desirable that the electrical conductors should. extend within the joint. Such coveredijoints were hitherto usually made in the form of half coverings, clamped together by means of a centre bolt. passed into the joint through an opening in one or the half coverings, and was passed in the form of a'bow through t. 9 covering on the one side of the centre bolt and out through another opening in the second half part of the covering. This arrangement, however, has proved to have serious disadvantages. As a matter of fact, it is normally required of a joint of this kind, that it should be possible to swivel it at least :90 from the straight line position, and for certain purposes, for instance more complicated electrical illuminating arrangements in tool machines, greater angles may be desired. The space within the coverings'is normally rather small and when the joint is swiveled or swung from one terminal position to another the electrical conductor passing the joint will be subjected alternatively either tolongitudinal tension or compression as the joint is swung over from one terminal position which-requires the least length of conductor to pass the joint to the other terminal position re- .quiring the greatest length of conductor to pass the joint, or vice versa. Experience now has proved that most of the insulated electrical conductors-and especially rubber insulated. electrical The conductors were conductors are subject to serious damage by such movements, whereas they are well able to withstand a pure bending or a pure turning. Smaller bending or turning movements are even believed to delay or prevent the hardening of the rubber, whereas on the other hand the above named pushing and pulling movements have the con.- trary action and further strongly contribute to the rubber insulation breaking or forming cracks. If the insulation is destroyed, short-circuiting at best will ensue, but it is not excluded that voltage carrying conductors will be connected to the metallic arm and thereby the worker, who is holding with his one hand the tool machine and with his other hand the armature arm, may get electrical voltage through his body, which may have a-deadly effect upon him. Therefore, it is of the utmost importance, that joints for electric light arms are made in such a way, that the electrical insulation material is to the utmost extent spared from such movements, which may destroy it.

Ehere has also been proposed an arrangement, in which the joint is formed by two half caps or coverings in the form of perpendicularly cut cylindrical bodies (see U. S. Patent No. 2,648,313). These were applied against each other, and one of the arms was connected to the cylindrical wall of the one cap, whereas the other one of the arms was connected to the other one of the caps. In this arrangement, however, the arms did not run mutually in longitudinal direction, and thereby certain circumstances appeared, which decreased toa-considerable extent the applicability of the swivel joint. Firstly, if the plane of the joint should be vertical, there would be required a rather great stillness of the joint, as the sidewards displacement between the two arms causes a bending moment in the adjustment of the joint. But the intention is, that such a great friction should be present in the joint surface, that the bracket should by means of this friction be kept in 'the:position to which which ithad been adjusted. The same friction, however, also hasto be overcome when the joint is adjusted, and the consequence therefore will be that such great bending actions will appear in the joint, that one has to make the joint considerably heavier and more bulky than is normally allowed for indoor lighting, in order to prevent its destruction.

Secondly, the side displacement of the joint means, an essential danger, when the j oint. for. instanceis used for machineillumination in a factory. The joint being in the form or" a hook, pref erably with sharpledseait may to. some extent be in the way of the workers movements, catch his clothes or in some other Way make the work at the machine dangerous to him.

Thirdly, it has been proved by experience from joints of the mentioned kind, which were used for rotation in the horizontal plane, that the friction surfaces were rather soon subject to an oblique wearing due to the bending moment, which requires a repeated adjustment of the friction pressure. If this adjustment of the friction pressure is not made in time, the wear may result in the friction surfaces becoming somewhat rounded. In this case the joint cannot be made to properly operate again by adjustment of the friction pressure, but all of the worn parts must be replaced. On the other hand, joints of the kind here in question are manufactured in mass production, and therefore the costs for changing separate parts usually will be unreasonably expensive, and therefore a joint worn in this manner usually must be replaced.

When the joint is for instance used for table lamps or the like, the base of which is loaded with a weight and not fixed to a wall or a similar surface, the bending moment will further cause a fourth disadvantage. Ihe friction required to hold the joint is so great that the joint cannot be adjusted with one hand, because the weighted base is not heavy enough to resist the force necessary to overcome the friction. The adjustment of the joint therefore requires the use of both hands.

For all these reasons joints of the above mentioned kind are not suitable for use except where the plane of movement was horizontal, and even in this case certain of the mentioned disadvantages remain. By the present invention the said disadvantages are done away with. The invention refers to a joint for electrical lighting arms, in which the electrical conductors are made sub-- ject only to such movements, which have proved not to be dangerous, and even in certain cases to be beneficial to the rubber insulation, and further any bending moment at the adjustment of the joint is avoided. According to the invention the two parts, moving against each other, are connected by means of a hOllow bolt of such dimensions that the electrical conductors may easily be drawn through the hollow bolt. Each of the two parts of the joint, moving in relation to each other, thereby is provided with a neck shaped part and a plate shaped part, and said parts are turned in such a way in opposite directions, that the electrical conductor after having been drawn through the one neck shaped part and the hollow bolt extends out through the other one of the neck shaped parts. Further the parts are shaped in such a way that the axial lines of the neck shaped parts substantially coincide with the friction level between the two plate shaped parts.

Thus the hollow bolt will run through the two plates, and the head of the bolt will press against one of the plates, whereas a nut, screwed on the hollow bolt will press against the other one of the plates. It is all a matter of whether the bolt turns with the first or the second of the two plate shaped parts, when the joint is moved. On the other hand the nut will probably turn with the plate against which it is pressed by friction, and it may therefore occur that the hollow bolt turns with the one and the nut with the other of the two plate shaped parts whereby the align-- ment pressure will change so that the joint either will become too light or too loose.

; fibrous material.

In the manufacture of the two parts, moving" against each other, it is further difficult to avoid sharp edges. Especially is this the case with respect to the two plate shaped parts, kept together by means of the hollow bolt. When moving the joint it may therefore happen, that sucha sharp edge slides on the electrical conductors and destroys their insulation. I

The last named two disadvantages are removed by means' of some details of the present invention, as will be evidentfrom the following description of one form of execution thereof, taken in connection with the annexed drawing, in which Fig. 1 is a longitudinal sectional view of the assembled joint;

Fig. 2, an elevational view of a hollow bolt for securing certain of the parts together;

Fig. 3, a side elevational view of the bolts shown in Fig. 2;

Fig. 4, an elevational view of one of the electrical connecting members utilized in the joint;

Fig. 5, an elevational view of the washer which is disposed between relatively rotatable parts of the joint;

Fig. 6, an elevational view of one of the protective members;

Fig. 7, a sectional view showing one of the cover members which forms one-half of the joint housing; and,

Fig. 8, a sectionalview on the line 8-8 of Fig. 7.

In the drawing I0 and I! are the terminals of the arms of the bracket, said arms being connected to each other by means of the joint. The joint mainly consists of two parts I2 and I3, which are equally arranged. Each part is at its one end formed into a connection part or neck I l and I5, respectively, for the arms ID and II, respectively, and at its other end into bored plates I6 and II, respectively. Between the plates It and Il, suitably a loose plate I8 is inserted, allowing relative turning of the plates I6 and I! with a suitable amount of friction. The plate It may for instance be made of some hard The three plates I6, I1 and I8 are connected to each other by means of a bolt I9 and a nut 20. The bolt I9 is hollow, and having a central opening which is sufficiently large to permit the electrical conductors to pass through it.

When assembling the joint, the electrical conductor is drawn through the neck I4, the hollow bolt I9 and the neck I5, as indicated by means of the dash-dot line 2 I.

The joint may suitably be covered, one half part of the covering being fixed to the neck I4 and the other half part thereof to the neck I5. Both of the coverings should be provided with slots of such extent that the two main parts I2 and I3 may easily be moved inside the slots. The two covers are indicated 22 and 23, respectively, and the two slots in each of the covers are indicated 24 and 25, respectively.

In order to prevent the hollow bolt I9 from moving in relation to the part I3, against which the nut 20 bears, the opening for the bolt through the part I3 is provided with a tooth 26, and the bolt with a corresponding groove 27. When the bolt is moved, therefore, the head of the bolt will turn on the part l2, whereas turning will not take place between the nut and the part I3. In order to prevent wear of the electrical conductors, there is further provided a protection plate 28 and 29, respectively, This plate, which should be flexible, is bent at one end in such a way that it fits snugly inside the neck M or l5, respectively, whereas its other end presses against the part I! or it, respectively, and protects this part from contact with the electrical conductors.

What is claimed:

1. In a swivel joint for connecting conduits of electrical fixtures, a pair of members, means at one end of each member for securing it to the respective conduit, the opposite end of each member being formed with an apertured friction surface normal to the axis of the joint, a hollow bolt extending through the apertures for frictionally retaining said surfaces in angularly adjusted position, and an insulated electrical conductor extending from one of said conduits through said hollow bolt and into the other conduit.

2. In a swivel joint for connecting conduits of electrical fixtures, a pair of members, means at one end of each member for securing it to the respective conduit, the opposite end of each member being formed with an apertured friction surface normal to the axis of the joint, a hollow bolt extending through the apertures for frictionally retaining said surfaces in angularly adjusted position, a cover divided into two parts, each part being secured to one of said members, and an insulated electrical conductor extending within said cover from one of said conduits through said hollow bolt and into the other conduit.

3. In a swivel joint for connecting conduits of electrical fixtures, a pair of generally flat arms, means at one end of each arm for securing it to the respective conduit, the opposite end of each arm being formed with an apertured friction surface normal to the axis of the joint, a hollow bolt extending through the apertures for frictionally retaining said surfaces in angularly adjusted position, a cover divided into two parts, each part being secured to one of said arms and being formed with a slot for introduction of the arm during assembly of the joint, and an insulated electrical conductor extending within said cover from one of said conduits through said hollow bolt and into the other conduit.

4. In a swivel joint for connecting conduits of electrical fixtures, a pair of members, means at one end of each member for securing it to the respective conduit, the opposite end of each member bein formed with an apertured friction surface normal to the axis of the joint, a hollow bolt extending through the apertures and having a head bearing against one of said members, a

nut threaded on said bolt and bearing against the other of said members, cooperating means on said bolt and on said other member for preventing turning of the bolt relative to said other member, and an insulated electrical conductor extending from one of said conduits through said hollow bolt and into the other conduit.

5. In a swivel joint for connecting conduits of electrical fixtures, a pair of members, means at one end of each member for securing it to the respective conduit, the opposite end of each member being formed with an apertured friction surface normal to the axis of the joint, a hollow bolt extending through the apertures for frictionally retaining said surfaces in angularly adjusted position, an insulated electrical conductor extending from one of said conduits through said hollow bolt and into the other conduit, and a protecting plate disposed between each of said members and said conductor.

6. In a swivel joint for connecting conduits of electrical fixtures, a pair of arms, one end of each arm having a circular portion for securing it to the respective conduit, the opposite end of each arm being formed with an apertured friction surface normal to the axis of the joint, a hollow bolt extending through the apertures for frictionally retaining said surfaces in angularly adjusted position, an insulated electrical conductor extending from one of said conduits through said hollow bolt and into the other conduit, and a protecting plate disposed between each of said arms and said conductor, one end of each plate having a circular portion secured within the circular portion of each arm.

STIG THORSTEN CEDERBORG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 451,300 Drew Apr. 28, 1891 525,670 Segade et a1. Sept. 4, 1894 598,202 Harrell Feb. 1, 1898 809,432 Darrschmidt Jan. 9, 1906 1,693,443 Holt Nov. 27, 1928 1,822,260 Adams Sept. 8, 1931 FOREIGN PATENTS Number Country Date 351,537 Germany Apr. 8, 1922 

